1. Field of the Invention
The present invention relates to a driving waveform generating device and a driving waveform generating method for an ink-jet recording head capable of forming dots different in gradation value by driving the recording head according to gradation data, and more particularly to a driving waveform generating device and a driving waveform generating method for an ink-jet recording head capable of generating driving waveforms in a programmable fashion by only changing coordinate data to be prestored.
2. Related Art
A typical ink-jet printer has a recording head with many nozzles in the subscanning direction (vertical direction) and while paper is fed as designated, the recording head is moved by a carriage mechanism in the main scanning direction (horizontal direction) in order to obtain desired print results. An ink drop is discharged from each nozzle of the recording head at predetermined timing according to dot pattern data resulting from developing the print data fed from a host computer, and the data is put into print when the ink drops land on and stick to a print recording medium such as printing paper. Since the ink-jet printer is designed to discharge ink drops or stop to discharge them, that is, designed to control the on-off of dots, it is incapable of directly producing a print output in halftone; namely, gray color and the like. In consequence, there have heretofore been adopted a method of realizing halftone by expressing one pixel with a plurality of dots such as 4xc3x974, 8xc3x978 and so forth, and a technique of increasing the gradient by causing one nozzle to discharge ink drops different in weight dot by dot so as to variably control the dot diameter on printing paper. In order to cause one and the same nozzle to discharge a plurality of ink drops different in weight, it is needed to vary the driving waveform of the head accordingly.
In a conventional driving waveform generating method for an ink-jet recording head, a circuit constituted of a hybrid IC, for example, has been employed so that a desired driving waveform is generated by putting an electric charge in and out of a pressure generating element (piezoelectric vibrator) forming the output side of a head driving circuit in the pulse width modulation (PWM) system (charge pump system).
FIGS. 13(a), (b) are conceptual drawings of a conventional head driving circuit and the driving waveform formed thereby.
As shown in FIG. 13(a), the conventional head driving circuit is such that a piezoelectric vibrator C for discharging ink drops by displacing itself on receiving voltage forms a capacitor on the output side and is also connected to resistors R1-R6 different in resistance value. The connections of the piezoelectric vibrator C to the resistors R1-R6 are switched by transistors, respectively. The ON/OFF of these transistors are controlled by pulses in the aforesaid PWM system.
With respect to the driving waveform thus generated, the voltage is, as shown in FIG. 13(b), determined by the ON time (pulse width in the PWM system) of each transistor, and its inclination is determined by the CR constant at the connection of each of the resistors R1-R6 to the aforesaid piezoelectric vibrator C.
In the aforesaid driving waveform generating method using the PWM system, however, the use of a complicated timing pulse is required to obtain the desired waveform.
As obvious from FIG. 13(a), moreover, there has existed a great deal of trouble for regulating timing with respect to variations in component elements such as the resistors R1-R6. In order to obtain more gradation expressions now, it has been attempted to multivalue dots. However, the driving waveform tends to become more complicated if such multivalued dots are employed and this makes it difficult to deal with such a driving waveform in the conventional driving waveform generating system.
An object of the present invention made in view of various problems posed as stated above is to provide a driving waveform generating device and method for an ink-jet recording head so that a desired programmable driving waveform is obtainable through a simple operation.
Another object of the present invention is to provide a driving waveform generating device and method for obtaining many complicated driving waveforms to make it possible to acquire more gradation expressions.
In order to accomplish the objects above, a driving waveform generating device for an ink-jet recording head according to the present invention for use in retaining a group of waveform data for generating driving waveforms beforehand, selecting and reading at least one waveform data to be utilized out of the group of waveform data, subjecting the read waveform data to a predetermined arithmetic process in order to create the driving waveform, subjecting the signal with the driving waveform to D/A conversion, amplifying and outputting the converted signal.
According to the present invention, a driving waveform generating device for an ink-jet recording head, the driving waveform generating device generating at least one presumed driving waveform in order to drive the recording head according to gradation data by utilizing the driving waveform, the driving waveform generating device comprising: waveform data storage means having a group of coordinate data for generating the driving waveform; waveform data read means for selecting at least one utilizing waveform data from the waveforms and reading the group of coordinate data for the driving waveform; waveform data interpolation means for creating the driving waveform by interpolating point-to-point values into the group of coordinate data read by the waveform data read means; digital/analog conversion means for subjecting data on the driving waveform created by the waveform data interpolation means to digital/analog conversion in order to output an analog signal; and signal amplification means for amplifying the analog signal which has been output from the digital/analog conversion means.
The group of coordinate data for generating driving waveforms are retained beforehand, and the group of coordinate data on the driving waveform to be utilized according to the gradation data are read out and employed. Therefore, the programmable driving waveform can be generated only by changing the group of coordinate data retained beforehand. Since the point-to-point values are interpolated in the group of coordinate data, the creation of the driving waveform can be made possible. The interpolated coordinate data is subjected to the D/A conversion. The signal subjected to the D/A conversion is amplified up to the level at which it is capable of driving the head, and the desired programmable driving waveform is obtainable through the simple operation, whereby the predetermined driving waveform in the form of a complete shape can be generated.
According to the present invention, a plurality of groups of coordinate data are prepared; any one of the groups of coordinate data are read; and a proper driving waveform corresponding to the gradation data is created so as to drive the recording head by utilizing the driving waveform.
According to the present invention, one driving waveform is created by reading out the group of coordinate data; and parts of the driving waveform are selectively utilized so as drive the recording head according to the gradation data.
According to the present invention, the driving waveform corresponding to the gradation data is created properly by selectively reading parts of the group of coordinate data so as to drive the recording head by utilizing the driving waveform.
According to the present invention, in the case of a gradation for forming dots by utilizing the driving waveform, a trapezoidal wave is contained in a driving waveform to be created.
According to the present invention, in the case of a gradation without forming dots by utilizing the driving waveform, a driving waveform to be generated is linear.
According to the present invention, the driving waveform generating device further comprises compensation means for correcting the coordinate data in consideration of ink condition during a printing operation.
Therefore, the desired driving waveform can be generated correctly because the coordinate data is corrected in consideration of the ink condition during the printing operation even when there occurs the difference in the environmental condition between the group of prestored coordinate data for generating the driving waveform and the actual printing operation.
According to the present invention, the ink condition is taken into consideration during the printing operation based on at least environmental temperatures.
Therefore, even though the environmental temperature during the printing operation differs from the temperature at the time the driving waveform is presumed, the desired driving waveform fit for use as the environmental temperature can be generated.
According to the present invention, the ink condition is taken into consideration during the printing operation based on at least environmental humidity.
According to the present invention, the signal amplification means comprises an amplifier circuit including a pair of transistors whose mutual emitters are connected together, and fixed resistors for always applying a predetermined voltage between the base.emitter to make the pair of transistors operate in an active area; and a negative resistor element having the same resistance value as that of the fixed resistor is connected in parallel to by-pass the fixed resistor at a reference temperature before the pair of transistors self-generate heat so as to decrease the voltage between the base.emitter when the voltage between the base.emitter rises because of the self-generation of heat on the part of the pair of transistors.
While the waveform is amplified in an extremely short time by operating the transistor in the active area, the negative resistance element is used for lowering the resistance value even though the self-generation of the transistor occurs to reduce the voltage between the baseemitter, whereby the thermal runaway of the transistor is prevented.
A thermistor may be employed as the aforesaid negative resistance element.
According to the present invention, while a group of data on partial waveforms for generating driving waveforms are retained, a plurality of partial utilizing driving waveforms are selected from the group of data on the partial waveforms in order to create a driving waveform by combining the partial waveforms.
A programmable driving waveform may be generated by changing the group of data on the partial waveforms to be retained beforehand or by selecting some of them or otherwise changing the way of combining them.